1. Field of the Invention
The invention relates to a heater plug for Diesel engines or internal combustion engines without spark ignition, particularly for use as a preheating cold-starting aid.
2. Discussion of Prior Art
The state of the art in this area has been reviewed extensively in the article by Helmet Weil entitled "Anlasshilfsmittel fur Dieselmotoren" (Starting aids for diesel engines) in the journal BOSCH Technische Berichte, vol. 5, Nos. 5-6, pp. 279 to 286. The term heater plug is applied to both the hot-wire plug and the hot-pin plug. In the section on starting aids in the combustion chamber, a hot-pin plug is described and illustrated in FIG. 3; and a high-intensity hot-pin plug shown in FIG. 8 is described as a starting aid in the intake manifold. In both cases a heater coil is used which is embedded by means of an insulating magnesium oxide powder in a heater tube made of heat-resistant steel. The heater coil itself is made of a resistance material on a nickel-chromium or chromium-iron-aluminum basis.
In FIG. 4, temperature and current are plotted against time. Accordingly, the preheating time of prior-art heater plugs ranges from 10 to 50 sec, depending on the ambient temperature. These preheating times are based on an ambient temperature between about +20.degree. and -20.degree. C. In colder weather, however, preheating times of up to 2 minutes have been observed in practice. It has been sought to reduce these times by the use of special electrical auxiliary apparatus, such as a current regulator. This approach, however, is rather costly.
It is an object of this invention, therefore, to provide a heater plug which has a reduced preheating time also when used in winter in northern latitudes, for example.